The present invention relates to a tensioner for tensing belt or chain adequately by using urging tensioning a rod, more particularly to such tensioner having a compression spring for urging tension rod.
This type of tensioner has shown the following problems: when a tension rod is excessively urged and does not return due to the excessive variation of driving torque, the belt or chain becomes excessively tensioned sometimes causing buzzing or until causing excessive wear on itself. Taking this undesirable situation in consideration, a tensioner 100 has been disclosed by the Japanese Utility Model Application Laid-open No. 62-13257 whereby said tension rod has been provided with a restoring capacity.
As shown in the FIG. 4, the tension rod 101 of tensioner 100 for tensioning a chain is mounted in a casing 104 so as to be urged freely by a compression spring 105. The tension rod 101 is formed with a rack on its side and the mating pawls of ratchet 102 are engaged with the rack. A shaft 103 fixed on the ratchet 102 is inserted in the vertical slot 106 so that the ratchet pawls may slip on the rack to change its position. When the chain is slackened, normally the tension rod 101 advances to keep adequate tension on it, the wack or returning stroke of tension rod 101 is controlled by the ratchet pawl 102. On the other hand, when the chain is excessively tensioned due to the excessive advance of tension rod 101, the shaft 103 of the ratchet works to alleviate excessive tension.
Hereinafter the problems to be solved by the invention will be explained. Since the back stroke of tension rod 101 is controlled by the ratchet pawl 102, the shaft 103 and vertical slot 105 as aforementioned, the back stroke of the tension rod 101 excessively urged by the resonant amplitude of belt or chain is reduced and when the shaft 103 of ratchet pawl hits on the bottom of vertical slot 106 after coursing the full stroke of slot, the tension rod 101 does not function to alleviate excessive tension of chain or chain because the tensioner turns only a rigid object against the counterforce of belt or chain.
The present invention has been developed considering the above situations and is to provide a tensioner having a prompt response to slackening, an ability to alleviate excessive tension on belt or chain and a simple and compact construction.